MANILA, Dec. 13 (Xinhua) -- The Philippine Congress approved Philippine President Rodrigo Duterte's request on Wednesday to extend the martial law in Mindanao for another year to "quell completely" the terrorist and rebels in the southern Philippine region.

After debating for more than four hours in a special joint session, lawmakers overwhelmingly approved Duterte's request - in a vote of 14-4 in the Senate and 226-23 in the House of Representatives - to keep Mindanao under military rule until December next year.

Duterte initially imposed a 60-day martial law in Mindanao on May 23, after Islamist fighters who have pledged allegiance to Islamic State laid siege to Marawi, a predominantly Muslim city in Mindanao.

At the height of the intense fighting to retake Marawi from the pro-IS militants in July, Duterte asked Congress to extend the martial law until December 2017, a request that lawmakers easily approved.

Five months after the attack, the government managed to retake the besieged city in October, paving the way for the reconstruction of the ruined city.

Executive Secretary Salvador Medialdea, who attended the joint session, said placing Mindanao further under martial rule would allow the government troops to protect the region while the rehabilitation and reconstruction is underway.

"We do not ask for an unlimited martial law. What we are seeking is an unlimited peace," he told the lawmakers.

Duterte formally requested the Congress on Monday to extend martial law in the entire Mindanao until Dec. 31, 2018 in order to "quell completely" the threat of terrorism in southern Philippines.

In a letter addressed to Congress, Duterte said "a further extension of the implementation of martial law and suspension of the privilege of the writ of habeas corpus in Mindanao will help (the government security forces) quell completely and put an end to the ongoing rebellion in Mindanao."

Duterte said placing Mindanao under martial law for another year will also prevent violent extremism from spreading to other parts of the country.

Duterte said he based his decision from the recommendation of Defense Secretary Delfin Lorenzana, also the martial law administrator.

Citing the security assessment of the Armed Forces of the Philippines, Lorenzana said extending martial law in Mindanao for another year will ensure total eradication of DAESH-inspired Da'awaful Islamiyah Waliyatul Masriq (DAWM), other like-minded local and foreign terrorist groups and armed lawless groups, and the communist rebels and their coddlers, supporters, and financiers.

Moreover, Duterte said that militants continue "to rebuild their organization through the recruitment and training of members and fighters to carry on the rebellion" despite the death of extremist leaders Isnilon Hapilon and the Maute brothers.

The president said IS-linked militants "have been monitored" to conduct "radicalization" through active recruitment, financial and logistical buildup and consolidation in central Mindanao particularly in Maguindanao and North Cotabato provinces, and Sulu and Basilan, the remote island provinces off Mindanao and known hideout of militants.

He said other IS-inspired groups Bangsamoro Islamic Freedom Fighters (BIFF) and the Abu Sayyaf Group (ASG) are also planning to sow terror in the impoverished region.